A planetary gear assembly converts an input rotation to an output rotation. Typically, a gear ratio of the planetary gear assembly is configured such that the output rotation has a different angular velocity and torque than the input rotation. In one application, a planetary gear assembly is coupled to the rotational output of an electric motor. The planetary gear assembly may be used to convert the rotational output of the electric motor to a rotational output having torque and angular velocity characteristics suitable for the particular application.
The typical planetary gear assembly includes a sun gear, numerous planet gears, and a ring gear. The sun gear has a toothed exterior periphery and defines a central axis. The planet gears each have a toothed exterior periphery that is configured to mesh with the toothed exterior periphery of the sun gear. The ring gear, which is sometimes referred to as an annulus, has a toothed interior periphery that is configured to mesh with the toothed exterior periphery of the planet gears. The ring gear has a central axis, which is coaxial with the central axis of the sun gear. Some planetary gear assemblies also include a carrier, which is connected to each of the planet gears. The carrier also defines a central axis, which is coaxial with the central axis of the sun gear.
Operation of a planetary gear assembly that includes a planet gear carrier involves (i) fixing the position of one of the ring gear, the carrier, and the sun gear; (ii) rotating another one of the ring gear, the carrier, and the sun gear; and (iii) generating a rotational output at the remaining one of the ring gear, the carrier, and the sun gear. For example, in one configuration, the ring gear is maintained in a fixed position, the sun gear receives an input rotation, and an output rotation is generated at the planet carrier, which rotates about its central axis.
In general, planetary gear assemblies are designed and machined to introduce a particular gear ratio between the input rotation and the output rotation. Therefore, most planetary gear assemblies are application specific devices. In view of the foregoing, it would be desirable to utilize a particular planetary gear assembly in multiple applications. However, parameters such as input angular velocity, input torque, output angular velocity, output torque, and maximum operating speed, often restrict the potential use of a planetary gear assembly to only a limited number of applications. In addition, the continuing desire to increase the efficiency of electric products makes it desirable for electric motors and planetary gear assemblies to generate more output torque with a system that occupies less space. Accordingly, further advancements are desirable for planetary gear assemblies.